Along with the respect to life quality and the rise of environmental protection consciousness, at present, the trend that the biological insecticides are substituted for the traditional pesticides to prevent the ultimate accumulation in the food chain has become the mainstream, in which Bacillus thuringiensis is the most famous application in the biological insecticides, and is easily utilized and safe.
Bacillus thuringiensis, a Gram-positive rod bacterium, is an insectile pathogenic bacterium. B. thuringiensis will progress into the non-mitotic semi-stationary phase or differentiate to form the spore or the insecticidal crystal protein while lacking nutrient or staying in the worse environment. The insecticidal crystal protein produced from B. thuringiensis can inhibit the growth of some insect pests, but is not harmful to mammals and birds. Therefore, scientists have been isolated various insecticidal genes from B. thuringiensis, and developed as the recombinant genetic products.
The endotoxin gene of B. thuringiensis is located on the plasmid thereof, so as to proceed the generic engineering easily. In the early stage, the recombinant endotoxin genes almost are limited in the cloning of single gene fragment. Recently, the multiple endotoxin genes or the genes with large diversities, even the chimeric genes, are utilized so as to improve the insecticidal effect, enlarge the insecticidal area or modify the resistance of B. thuringiensis to the worse environment.
The parental relationships among various endotoxin proteins of B. thuringiensis are different because of the insecticidal crystal proteins produced from the divergent nucleotide sequences of plasmids thereof. The insecticidal targets also are different, which are classified as six groups (Hofte and Whiteley, 1989; Gill et al., 1992; Gleave et al., 1993; Lereclus et al., 1993; Shin et al., 1995; and Kostichka et al., 1996). Among these literatures, Cry1 protein family has the insecticidal effect to Lepidoptera; Cry2 protein family shows the insecticidal effect to Lepidoptera and Diptera, or only has the insecticidal effect to Diptera; Cry3 protein family has the insecticidal effect to Coleoptera; and Cry4 protein family only has the insecticidal effect to Diptera. Cry5 protein family cannot form as crystal protein, whereas Lepidoptera and Coleoptera can be killed by some part of Cry5 proteins but cannot be killed by other part thereof. CytA protein does not have specific insecticidal scope; however, the cytolytic and hemolytic effects can be induced by CytA protein. The cry1 gene of B. thuringiensis encodes the longest amino acid sequence, but cytA gene thereof encodes the shortest one.
U.S. Pat. Nos. 5,827,514 and 5,965,428 respectively disclose Cry1Ac and Cry1F chimeric proteins with different fragments for insecticidal function. U.S. Pat. No. 7,070,982 further discloses the composite proteins of Cry1Ab, Cry1Ac and Cry1F. Taiwan Patent No. 224139 further discloses a single bacterial strain containing cry1Aa, cry1Ab, cry1C and cry1D gene fragments. From the abovementioned references, the insecticidal effect of the multiple endotoxin gene products is large better than the function of the single endotoxin gene product for antagonizing insect pests.
Therefore, scientists are still exploring the microorganism with multiple endotoxin genes isolated by generic engineering or isolated by natural selection.
It is therefore attempted by the applicant to deal with the above situation encountered in the prior art.